Unemployed men queue for coffee and bread at a soup kitchen in New York, during the Great Depression.
Photograph: FPG/Getty Images

Wealth inequality in the US is at near record levels according to a new study by academics. Over the past three decades, the share of household wealth owned by the top 0.1% has increased from 7% to 22%. For the bottom 90% of families, a combination of rising debt, the collapse of the value of their assets during the financial crisis, and stagnant real wages have led to the erosion of wealth.

The share of wealth owned by the top 0.1% is almost the same as the bottom 90%

The share of wealth owned by the top 0.1% is almost the same as the share owned by the bottom 90%

The picture actually improved in the aftermath of the 1930s Great Depression, with wealth inequality falling through to the late 1970s. It then started to rise again, with the share of total household wealth owned by the top 0.1% rising to 22% in 2012 from 7% in the late 1970s. The top 0.1% includes 160,000 families with total net assets of more than $20m (£13m) in 2012.

In contrast, the share of total US wealth owned by the bottom 90% of families fell from a peak of 36% in the mid-1980s, to 23% in 2012 - just one percentage point above the top 0.1%.

There is a new wealth divide in the US

Average wealth of families in the bottom 90% and the top 1% of the wealth distribution, in constant 2010 US dollars, 1946-2012 Photograph: Emmanuel Saez and Gabriel Zucman

The growing indebtedness of most Americans is the main reason behind the erosion of the wealth share of the bottom 90%, according to the report’s authors. Many middle-class families own their homes and have pensions, but too many have higher mortgage repayments, higher credit card bills, and higher student loans to service. The average wealth of bottom 90% jumped during the stock market boom of the late 1990s and the housing bubble of the early 2000s. But it then collapsed during and after the most recent financial crisis.

Since then, there has been no recovery in the wealth of the middle class and the poor, the authors say. The average wealth of the bottom 90% of families is equal to $80,000 in 2012— the same level as in 1986. In contrast, the average wealth for the top 1% more than tripled between 1980 and 2012.

Income inequality across the G20 is worrying, Oxfam warns

Income inequality in the G20 Photograph: Oxfam

Among the nine G20 countries with sufficient data (featured in the graph above), the richest 1% of people (by income) have increased their income share significantly since 1980, according to Oxfam. In Australia, for example, the top 1% earned 4.8% of the country’s income in 1980. That had risen to more than 9% by 2010.

Oxfam says that in the time that Australia has held the G20 presidency (between 2013 and 2014) the total wealth in the G20 increased by $17tn but the richest 1% of people in the G20 captured $6.2tn of this wealth – 36% of the total increase.